1. Technical Field
The present disclosure generally relates to a method and associated instrumentation for insertion of spinal implants to facilitate fusion of adjacent vertebral bodies and, more particularly, to a vertebral spacer utilized to maintain a predetermined spacial distance of adjacent vertebrae during the implant insertion.
2. Background of the Related Art
A large number of orthopedic procedures involve the insertion of either natural or prosthetic implants into bone or associated tissues. These procedures include, for example, ligament repair, joint repair or replacement, non-union fractures, facial reconstruction, spinal stabilization and spinal fusion. In a typical procedure, an insert, dowel or screw is inserted into a prepared bore formed in the bone or tissues to facilitate repair and healing. See, for example, U.S. Pat. No. 5,470,334 to Ross et al.; U.S. Pat. No. 5,454,811 to Huebner; U.S. Pat. No. 5,480,403 to Lee et al.; U.S. Pat. No. 5,358,511 to Gatturna et al.; and U.S. Pat. No. 4,877,020 to Vich.
Some implants are particularly configured with cavities and bores to facilitate bony ingrowth and enhance anchoring of the implant at the insertion site. See, for example, U.S. Pat. No. 4,328,593 to Sutter et al.; U.S. Pat. No. 4,936,851 to Fox et al.; and U.S. Pat. No. 4,878,915 to Brantigan. Other specialized implants include fusion cages having internal cavities to receive bone growth stimulation materials such as bone chips and fragments. See, for example, U.S. Pat. No. 4,501,269 to Bagby; U.S. Pat. No. 4,961,740 to Ray et al.; U.S. Pat. No. 5,015,247 to Michaelson; and U.S. Pat. No. 5,489,307 to Kuslich et al. These types of implants are particularly well suited for intervertebral spinal fusion procedures necessitated by injury, disease or some degenerative disorder of the spinal disc. Subsequently, there may be progressive degeneration leading to mechanical instability between adjacent vertebrae necessitating direct fusion of the vertebrae while maintaining a pre-defined intervertebral space. This fusion may be accomplished by the insertion of one or more of the specialized implants as discussed above and also discussed in commonly assigned U.S. Pat. No. 5,026,373, the contents of which arc incorporated herein by reference.
Both anterior (transabdominal) and posterior surgical approaches are used for interbody fusions of the lumbar spine. Fusions in the cervical area of the spine are performed using an anterior or posterior approach. Typically, an implant such as a plug, dowel, prosthesis or cage is inserted into a preformed cavity or drilled bone inside the interbody, interdiscal space. Since it is desirable in these procedures to promote a "bone to bone" bridge, connective tissue and at least a portion of the distal tissue is removed. Preferably, relatively deep cuts are made in the adjacent bones in order to penetrate into the softer, more vascularized cancellous region to facilitate bone growth across the implant.
In many surgical implant techniques, two implants are inserted within the intervertebral space in side-by-side or lateral relation to fully support the adjacent vertebrae across the span of the intervertebral space. In accordance with these techniques, a first lateral side of the intervertebral space is prepared, e.g., by removing excess disc material and drilling/tapping a bore to receive the implant followed by insertion of the implant. Thereafter, the second lateral side is prepared for implant insertion in the same manner. During the initial preparation of the first lateral side of the intervertebral space, however, the adjacent vertebrae are subjected to displacement in both the lateral and longitudinal direction. This may cause additional movement of the vertebral portion disposed on the other (second) lateral side of the intervertebral space.
U.S. Pat. No. 5,489,307 to Kuslich discloses a surgical method for implanting at least two spinal implants into a disc space utilizing a solid cylindrical distraction spacer which is inserted initially within one side of the disc space. The rigid distraction spacer is intended to act against the vertebral end plates of the adjacent vertebrae to urge the vertebra apart. The spacer is sized to be fully inserted such that it is either flush or slightly recessed within the disc space.
The method and device disclosed in the Kuslich '307 patent is subject to several disadvantages which detract from its usefulness particularly in spinal surgery. For example, the Kuslich '307 distraction spacer is cylindrical thereby providing a limited area of surface contact with the adjacent vertebrae, which, consequently detracts from the stability provided to the adjacent vertebrae. Secondly, the distraction spacer is sized for complete entry within the intervertebral space, i.e., no provision is made to limit the insertion distance within the space. Consequently, over-insertion of the Kuslich distraction spacer may cause undesirable contact with, e.g., the aorta or dural nerve, depending on the surgical approach. Thirdly, the Kuslich '307 distraction spacer requires complete insertion within the intervertebral space which due to the concavity of the disc space, impedes attempts to subsequently remove the spacer after the operation.
Accordingly, the present disclosure is directed to a novel method and associated instrumentation which overcomes the disadvantages of the prior art. The novel method and instrumentation of the present disclosure facilitates the introduction of a fusion implant by stabilizing the adjacent vertebrae and providing parallel vertebral endplate distraction so as to reestablish intervertebral disc space height during implant insertion and/or the performance of other spinal procedures.